1. Field of the Invention
The present invention relates to an internal combustion engine having a system for controlling the engine""s compression ratio by means of a dual purpose lubricating oil pump having variable pressure output.
2. Disclosure Information
For many years, engine designers have desired to implement variable compression ratio control systems for use with reciprocating internal combustion engines. The ability to control an engine""s compression ratio is desirable because it is well known that higher compression ratios promote superior fuel economy, but at the expense of knocking operation in the event of either excessive engine loading or inferior quality fuel. With a variable compression ratio system, it is possible to run at an higher compression ratio during low engine load and to alter the compression ratio to operate at a lower compression ratio during operation at higher engine loads. Moreover, if variable compression ratio control capability is coupled with the ability to boost the engine such as through the use of a supercharger, very high specific output maybe achieved at high loads, while preserving the capability to obtain superior fuel economy with higher compression at lower loads.
Many types of variable compression ratio designs have been proffered. Some systems such as those proposed by the BICERI organization change the compression height of the piston through use of hydraulic elements. Other systems change compression height of the piston through the use of a elastic element such as a Belleville spring interposed between the crown of the piston and its main body.
U.S. Pat. No. 6,394,047B1, which is assigned to the assignee of the present invention, and which is hereby incorporated by reference in this specification, discloses and claims a variable compression ratio connecting rod which employs a grooved bearing to pick up an oil pressure switching signal from the crankshaft of the engine. The present invention deals with a system for providing that signal to the crankshaft.
Although there are known systems for providing a high pressure oil signal to a variable compression ratio system in an engine, such systems typically use an external pump or an added hydraulic pump having significantly greater complexity than pumps currently found on engines. These additional pump systems typically include numerous check valves, solenoid valves, hydraulic accumulators, additional pumping elements and other devices which greatly increase the cost of a variable compression ratio system. In contrast, the present system utilizes the engine driven lube oil pump as a dual purpose, multi-pressure device. In other words, only the single pump is needed. Moreover, the present system does not use any uniquely dedicated control passages. In another words, all of the oil passages are used for normal lubrication, with two of the passages having dual roles for use as both lubrication and control signal passages.
A variable compression ratio control system for an internal combustion engine includes a lubrication system for selectively providing oil to connecting rods within the engine at both a lubrication pressure and at a control pressure. A plurality of compression ratio adjusters is responsive to the pressure of lubricating oil being provided to the connecting roads through the lubrication system. One of the compression ratio adjusters is associated with each of the connecting rods. A lubricating pump provides lubricating oil to the connecting rods through the lubrication system. The lubricating pump is selectively operable at either the lubricating pressure or the control pressure.
The present system further includes a controller for sensing a plurality of engine operating parameters and for operating the lubricating pump at a pressure level which is dependent at least in part upon the sensed values of the engine operating parameters. The controller operates the lubricating pump and the valves of the variable compression ratio control system to cause the compression ratio adjusters to adjust to a lower compression ratio at higher engine loads and to a higher compression ratio at lower engine loads.
According to another aspect of the present invention, a lubricating pump comprises a supply element and a pressure relief element, with the pressure relief element being controllable so as to determine the pressure of lubricating oil discharged by the lubricating pump to the lubrication system. The supply element and pressure relief element are preferably located within a common housing, with the pump itself being driven by the engine.
According to another aspect of the present invention, the lubricating pump has an integral pressure regulator which comprises an elastic element for maintaining oil discharge pressure during normal operating condition and an electronically controlled valve for increasing discharge pressure when the compression ratio is being changed.
According to another aspect of the present invention, a compression ratio control system includes a lubrication system for providing lubricating oil to a plurality of components within an engine, with the lubrication system having a main bearing oil supply passage which is bifurcated into two passages such that the first group of main bearings is provided with oil by one of said passages, and a second group of main bearings is provided with oil by the other said passages. A plurality of compression ratio adjusters is responsive to the relative pressures of the lubricating oil being provided to the first and second groups of main bearings through the bifurcated oil passages. The compression ratio adjusters are switchable between a higher compression ratio and a lower compression ratio. The lubricating pump provides oil at a lower pressure during normal operation of the engine and at a higher pressure when the compression ratio adjusters are being switched from one compression ratio to the other compression ratio.
It is an advantage of the present invention that an engine may be equipped with a variable compression ratio controller without the necessity of adding another hydraulic pump with its attendant cost and complexity.
It is a further advantage of the present invention that implementation of a variable compression ratio control system according to this invention will necessitate only minor changes to many existing engine designs.
It is a further advantage of the present invention that the present system provides variable compression ratio with very little power consumption.
Other advantages, as well as objects and features of the present invention will become apparent to the reader of this specification.